1. Technical Field
This invention relates to a method for driving a surface emitting semiconductor laser, an optical transmission module, and a handheld electronic device.
2. Related Art
For an optical transmission module that is modulated at a high speed in a gigahertz or higher frequency band, a surface emitting semiconductor laser (Vertical-Cavity Surface-Emitting Laser diode: hereinafter referred to as VCSEL) that is designed to have a small internal resistance is typically used. Some of single-mode VCSELs have an internal resistance of greater than 50 ohms; for example, an internal resistance of several hundred or several thousand ohms. However, such a high resistant VCSEL has a higher resistance than a resistance of, for example, 50 ohms, that is typically used for a driving circuit or wiring and thus causes impedance mismatching.
For devices, such as handheld devices, that are susceptible to electromagnetic noises, the use of an optical transmission module in which a VCSEL is used as a light source for signal transmission has been considered. A major technical difficulty therein is the reduction in power consumption of the VCSEL. One method for reducing power is to lower the threshold current of the VCSEL and reduce the driving current However, in general, if the threshold current is lowered, the internal resistance becomes high, and thus it becomes difficult to drive the VCSEL at a high speed.
The present invention addresses the issues of related arts described above, and aims to provide a method for driving a surface emitting semiconductor laser at a high speed while reducing power consumption.
The present invention further aims to provide an optical transmission module that is appropriate for reducing power consumption of handheld devices or the like.